链接 c++代码：对 `Student::Student(std::__cxx11::basic_string, std::allocator>, double) 的未定义引用

Question

每次我构建代码时都会出现此错误。我尝试了不同的项目，但结果是一样的。它出现在vscode和CLion中；但是我在 上尝试了代码；它正在发挥作用。

#include <iostream>
#include <string>
using namespace std;

class Student{

private:
    std::string name;
    double grade;

public:
    //public constructor to reach it
    Student (std::string s, double g);

    void setName(std::string n){
        name = n;
    }

    void setGrade(double g){
        grade = g;
    }

    std::string pass(){
        //if grade greater than 60 print "yes" if not print "no"
        return (grade > 60 ? "yes": "no");
    }

    void printStatus(){
        cout << "name:" << name << endl;
        cout << "grade: " << grade << endl;
        cout << "Pass: " << pass() << endl; 
        cout << endl;
    }

};



int main(){

    Student Barrak("Barrak", 96);
    Barrak.printStatus();
    Barrak.pass();


    return 0;
};

这就是我得到的。

PS C:\Users\barra\Desktop\ab> cd "c:\Users\barra\Desktop\ab\" ; if ($?) { g++ main.cpp -o main } ; if ($?) { .\main }
c:/mingw/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: C:\Users\barra\AppData\Local\Temp\cc1itdQl.o:main.cpp:(.text+0x54): undefined reference to `Student::Student(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, double)'
collect2.exe: error: ld returned 1 exit status
PS C:\Users\barra\Desktop\ab> 

Answer 1

问题是您只声明了参数化构造函数Student (std::string s, double g);而不是定义它。因此链接器在需要时无法找到它，因此给出了上述错误。

要解决这个问题，您可以添加此构造函数的定义，如下所示：

class Student{

private:
   //other members as before

public:
    //DECLARATION FOR PARAMETERIZED CONSTRUCTOR
    Student (std::string s, double g);

    //other members as before

};

//DEFINE PARAMETERIZED CONSTRUCTOR
Student::Student (std::string s, double g): name(s), grade(g) //this uses constructor initializer list to initiliaze name and grade
{
    
}

可以看到修改后的程序的输出此处。

方法 2

您还可以在类内部定义参数化构造函数，在这种情况下它将隐式内联，如下所示：

class Student{

private:
    std::string name;
    double grade;

public:
    //DEFINITION FOR PARAMETERIZED CONSTRUCTOR
    Student (std::string s, double g): name(s), grade(g)
    {
        
    }

    //other members as before

};